Mirror and method for making the same



Patented Sept. 22, 1942 2,296,602 manor; AND METHOD non MAKING 'rns SAME Clarence H. Dragert, New York, N. Y.

No Drawing. Application April 5, 1940, Serial No. 328,054

8 Claims.

My invention relates to methods for backing mirrors and to the products produced thereby, and refers particularly to methods and products of the character described in which lead is em ployed as one of the ingredients of said backing processes and of the produced backed mirrors.

The usual method of producing mirrors is to place an adhering fllm, or thin, layer, of a re-' fleeting material, generally silver, upon one side of a sheet of glass and then place an adhering film, or thin layer, of a protecting material upon the exposed face of the reflecting material.

My invention relates to new compositions of matter adapted for application to the reflective material of a mirror as a protective material therefor, and methods for applying the same.

Silver is a comparatively highly reactive metal resulting in physical and chemical changes when subjected to atmospheric and light conditions and to electrical charges when subjected to the presence or contact of certain other metals, and hence it is evident that considerable care must be exercised in determining the properties of a backing, or coating, of a silvered mirror inorder to retain it in its original reflective properties.

From among the 'many well-known and recognized agents that affect the usefulness of a silver mirror backing, the following may be mentioned: light, the presence of moisture in the atmospheric air which contacts it, the presence of salts and acids in such moisture or air, the presence of hydrogen sulfide, the action of excessive temperatures and galvanic actions between the silver and the metal employed in the backing composition.

My invention presents a composition of matter adapted for the backing of mirrors which overcomes all of the above mentioned, and other, objectionable features and which comprises a composition of matter which is impervious to the transmission of light therethrough; prevents the deterioration of the silver backing due to atmospheric moisture, acids, alkalies and hydrogen sulfide; freedom from galvanic action between the silver and the metal of my composition and which has low heat conductivity.

Among the other properties of my composition of matter is its low cost of production, its strong adherence to the silver, its rapid drying properties, its freedom from moisture, its hardness, its freedom from brittleness, its non-liability to become detached or flaked off from the mirror during the operations of cutting the mirrored sheets and the evenness and completeness of the deposited film.

'Copper is in the metal usually employed for the backing of silvered mirrors, the copper being deposited either electrolytically or through the medium of a composition of flaked copper in a solution of shellac.

From among the objections incident to the electrolytic method, the following are mentioned: the process is slow and expensive, there is a strong liability of depositing a film with pinholes, and because of the relative positions of silver and copper in the electro-chemical scale, colored blurs and streaks frequently occur due to the galvanic action between the two metals.

From among the objections incident to the copper-shellac method, the following may be mentioned: the high heat conductivity of copper, the acid properties of shellac and the relative positions of silver and copper in the electro-chemical scale leading to the probability of galvanic action between the two metals, through accidental pin-holes or otherwise, and the brittleness and lack of moisture-proofness of shellac.

Ihave found, however, that metallic lead can be applied as a silver mirror backing under conditions which will overcome all of the abovementioned difliculties incident to the employment of copper.

The composition of matter of my invention comprises lead, a synthetic resin, a plasticizer and an organic volatile solvent, the properties of these chemicals being explainedlater.

By synthetic resins" I mean those synthetic resins which are condensation products of phenol with urea-formaldehyde, maleic rosin esters, ester gums, condensates of vinyl acetate, cumar, polystyrene and similar resins, which are soluble in the solvent employed, are free from fatty acids and other acidifying compounds are acid resistant, and are alkali resistant. The resins I employ have the further property of producing a hard but not brittle film in the following of my process.

By plasticizers" I mean those compounds which have a plasticizing effect upon my compositions of matter. They may be either liquids, oils or solids in their normal conditions, they may be organic or inorganic, they must be soluble in the solvent employed, must be practically free from fatty acids and other free acids.' They must be neutral. The free fatty acids present in vegetable drying oils, such as linseed oil, must be eliminated and such oils, therefore, must be heated as in the production of varnish without the use of lead, cobalt, manganese or other dryer, which are known as "blown oils," or they must ings, among which is gold. It will thus be. seen that by the composition be neutralized with lime, or small amounts of metallic salts such as zinc oxide, zinc carbonate,

carbonate, calcined magnesium or other similarly efiective neutralizing agent. They must stand "the standard copper-strip corrosive test, and must'be dielectric. Among the plasticizers compound well known in the mirror producing .industry, linseed oil, castor oil, soya oil, blown capable of dissolving the resin and the plasticizer,

adaptable for use in my compositionpof matter are Nevinol," a commercial name for an organic among which are ethyl alcohol, methyl alcohol, I

butyl alcohol, benzol, toluene, 'xylol'and other solvents'havin'g the above-mentioned properties.

My invention includes also the addition of mica to the lead because of its insulating properties.

I give the following as one method of my invention:

Thoroughly mix 1% grams of Nevinol," 10 grams of a suitable synthetic resin and '10 grams ethyl-cellulose and dissolve the mixture in 80 parts of toluol and parts of ethanol until the volume reaches 180 c.cs. To this solution add 70 grams commercial lead paste-and stir thoroughly 'until a complete dispersion of the lead is accomplished.

The composition of matter described 'above, in

.the' form thus produced or by dilution with additional solvent if desired, is then applied to the silver backing of the mirror by spraying, flushing or by any other suitable method.

' The ethyl-cellulose may be omitted, but I of said sheet into smaller pieces and which possesses the other desirable features set forth in this Specification. I

I do not limit myself to the particular quantities, chemicals and steps of procedure specifically set forth, as these are given. simply as a means for clearly describing my invention.

What I claim is:

1. A method of protectively coating the metallicreflecting film of a glass mirror or the like to protect the said refiective'film-from spoilage due to exterior influences which consists in applying to said reflective film a free flowing composition of matter comprising 'lead, synthetic resin, plasticizer, an organic volatile solvent for said resin and plasticizer, and a member of the group consisting of ethyl-cellulose, methyl-cellulose and nitro-cellulose.--

2. A method of protectively coating the metallic reflecting film of a glass mirror or the like to protect the said reflective film from spoilage due prefer to employ it because of its dispersing properties andits ability to hasten the dryingas it has the eflect of quickly removing the tacky" eiiect of the composition incident to the drying operation. The ethyl-cellulose may be substituted by other chemicals having similar properties among which are methyl cellulose and -nitrocellulose, all of which chemicals having the described properties, I refer to herein as dispersers." By "NevinoP I mean the productknown commercially under that name, which is a mixture of dicoumarol and diindene.

The Nevinol, the synthetic resin and the solvents mentioned in the above example can be replaced by the other similarly applicable compounds mentioned herein, without going beyond the scope of myinvention.

It is evident that more than one synthetic resin, plasticizer, and disperser may be used in to exterior influences which consists in applying to said reflective film a free flowing composition of matter comprising lead, synthetic resin, "Nevinol, an organic volatile solvent for said resin and Nevinol," and a member of the group and-nitro-cellulose. =3. A"method of protectively coating the metallic reflecting film of a glass mirror or the like to protect the said reflective film from spoilage due to exterior influences which consists in app ying to said reflective film a free flowing composition of matter comprising lead, synthetic resin, plasticizer,-alcohol, and a member of the group consisting of' ethyl-cellulose, methyl-cellulose and nitro-cellulose.

4. In a glass mirror having a metallic reflecting film upon one side thereof, a protective coating for said reflective film comprising lead, synthetic resin, Nevinol, and a member of the group consisting of ethyl-cellulose, methyl-celluloseand nitro-cellulose.

5. A method of protectively coating the metallic reflecting film of a glass mirror or the like to protect the said reflectivefilm from spoilage due to exterior influences which consists in applying to said reflective film a free flowing composition lic reflecting film of a glass mirror or the like to the formation of a composition of matter of my invention, and when I use these words in the singular they are intended to include more than a single such compound.

While I refer particularly to silver coated mirrors, my composition of: matter is also suitable for mirrors having other reflective. coatof matter of my invention, I produce a dielectric protective coating for the reflective backing,

which is chemically and physically inert to said protect thesaid reflective filmiromspoilage due to exterior influences which consists in applying to said reflective film a free flowing composition "of matter comprising lead, synthetic, resin,

Nevinol," an organic volatile solvent for said resin and Nevinolj, and ethyl-cellulose.

- 7. Amethod-of protectively coating the metallic reflecting film "of a glass mirror or the like to protect the said-reflective film from spoilage due to'exterior influences which consists in applying to said reflective film a free flowing composition of matter comprising lead, synthetic resin, plasticizer, alcohol, and ethyl-cellulose.

8. In a glass mirror having a metallic refiecting film upon one side thereof, a protective coating for said reflective film comprising lead, synthetic resin, Nevinol," and ethyl-cellulose.

' CLARENCE H.-DRAGERT.

consisting of ethyl-cellulose, methyl-cellulose. 

